Jonathan Batchelor

Despite growing concern over CT-related radiation exposure, measuring cumulative exposure from CT imaging in a standardized or formal way is not part of routine practice for ordering physicians in the emergency department, according to a presentation this week at the 2009 RSNA meeting.

"The use of CT in the U.S. has gone from three million CT scans performed annually in 1980 to more than 60 million in 2005," said Dr. Amita Kamath. "Little research has been done on quantifying cumulative exposure to CT, as well as associated radiation dose over time."

Kamath conducted a retrospective study at the University of California, San Francisco, of emergency patients who received a CT exam between October 2006 and March 2007. She and fellow author Dr. Rebecca Smith-Bindman assessed the cumulative use of CT within one year of a patient's ED visit, stratified by the reason for that patient's visit.

Their main outcome measures included the receipt of CT, receipt of repeated CT (defined as three or more CT exams within one year), and high radiation exposure (defined as a dose greater than 50 mSv).

The researchers identified the following groups from a cohort of 10,382 patients:

Overall, 28% of patients received at least one CT scan. This ranged from approximately 20% to 22% of patients with trauma and altered mental status to 85% of patients with renal stone disease and 70% of patients with pancreatitis, Kamath said.

"Among patients who underwent CT imaging, the mean number of CT exams performed over the one-year period was two and varied from 1.8 in patients with trauma and altered mental status to 1.4 in patients with renal stone disease and 2.7 in patients with pancreatitis," she said.

The investigators found that 4% of patients received radiation exposure in excess of 50 mSv, with renal stone disease and pancreatitis patients most likely to receive this high dose, Kamath said.

"There is a statistically significant increase in cancer at effective doses in excess of 50 mSv," she said.

The research partners uncovered some disturbing trends in their analysis. In comparison with an altered mental status patient, a patient with renal stone disease was approximately 60 times more likely to receive a CT scan. Compared with patients with altered mental status, patients with pancreatitis were 20 times more likely-and patients with renal stone disease were eight times more likely-to receive a radiation dose of more than 50 mSv during the one-year study period.

"Use of imaging with CT is variable in the ED," Kamath said. "Several nonemergent diagnoses, such as renal stone disease and pancreatitis, were associated with the greatest increase in likelihood of receiving a CT, undergoing repeat CTs, and receiving a high radiation dose. For patients who undergo repeat CTs, a discussion between the ordering physician and radiologist is imperative to ensure that the most appropriate study is performed. This is particularly important given that many of these patients receive multiphase abdominal CT protocols, which average 30 mSv per scan."

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Despite growing concern over CT-related radiation exposure, measuring cumulative exposure from CT imaging in a standardized or formal way is not part of routine practice for ordering physicians in the emergency department, according to a presentation this week at the 2009 RSNA meeting.

CT radiation dose shows wide variance in ED

Adding noncontrast and delayed-contrast series to abdominal/pelvic CT examinations appears common in routine clinical practice and represents a potential public health danger with no associated clinical benefit, according to a presentation Monday afternoon at the 2009 RSNA meeting.

"The recent events at Cedars-Sinai have reminded us that we are not doing everything we can to minimize radiation exposure," said Dr. Kristie Guite from the radiology department at the University of Wisconsin in Madison.

In October, the FDA and Cedars-Sinai Medical Center revealed that 206 stroke patients who received CT scans at the Los Angeles hospital were overdosed with radiation.

However, according to research Guite began as a medical student and has continued during her residency, the Cedars-Sinai experience with CT-based radiation overdose is not unique.

Guite has focused her attention on a potentially significant source of excess radiation that has not heretofore been examined: additional CT series (such as routine noncontrast or delayed-contrast scans) conducted during an exam that are not supported by the medical literature.

"Medical radiation exposure should be reduced to only that which is needed in order to make a diagnosis," she said.

Guite reviewed 500 abdomen and pelvis CT exams performed at outside institutions and submitted for tertiary interpretation for appropriateness (using the American College of Radiology criteria) and for radiation dose.

"Radiation dose was calculated using the ImPACT [London] CT dose calculator, and associated cancer risks were estimated using methods described in the 

," Guite said.

There were a total of 978 series for 500 patients. Guite noted that nonindicated multiphasic series were found in 52.2% of the exams, the most common being delayed phase imaging in 77.7% of them.

She reported that the mean total radiation dose per patient was 34 (± 24.1) mSv. The nonindicated series had a mean dose of 16.3 (± 9.4) mSv, which resulted in a mean excess dose of 11.3 mSv per patient for the entire study population.

According to Guite, using the linear-no-threshold model of radiation risk, these unnecessary CT sequences could be delivering a significant radiation burden to patients.

"Extrapolation of this dose over the total number of abdomen/pelvis CT scans performed each year in the U.S. would result in an excess lifetime attributable risk of 0.1% for those undergoing an abdomen/pelvis CT exam, or up to 23,000 radiation-induced cancer cases per year," she said.

Adding noncontrast and delayed-contrast series to abdominal/pelvic CT examinations appears common in routine clinical practice and represents a potential public health danger with no associated clinical benefit, according to a presentation Monday afternoon at the 2009 RSNA meeting.

Unnecessary sequences add to radiation burden

If it's round, has a hole in it, and isn't a bagel or donut in the break room, chances are it's a CD brought into the practice by a patient. According to Dr. Bradley Erickson from the Mayo Clinic in Rochester, MN, the use of compact discs to transfer diagnostic imaging data has seen a steady increase over the past decade.

Image exchange on portable media is a two-part process. There's the part where image data is sent out and the part where image data is brought in.

"In the spirit of the holiday season, I have to say that it is better to give than to receive. Sending out a CD is a fairly easy thing to do," Erickson said in a presentation at the 2009 RSNA on Monday morning. "But bringing them into the system has been a much more divisive process."

He reported that more than 90% of image data coming in from the outside is being delivered on CDs. In order to ease the import of CD-based imaging data into their institution, Erickson's team wrote a CD-receive application.

The tool has brought 346,000 exams into the Mayo system, which has allowed metrics to be determined on the growth of CD utilization and statistics to be generated on the integrity of the imported data.

Erickson said they currently see a 0.2% rate of CDs with data integrity problems. These can range from a disc that is unreadable to CDs with the wrong patient ID or patient data on them. A CD data integrity problem of 0.2% may seem small, but it translates to four patients per day, or nearly 1400 patients annually, he said.

In order to verify the integrity of data on a CD, the Mayo workflow requires that a patient verify his or her demographic information with that on the CD. This step has allowed the group to catch most patient ID and patient data errors before they are brought into Mayo's EMR and PACS.

Erickson said that data CDs are showing up with greater frequency in his practice, at an almost 10% annual growth rate. And he expects they will enjoy a long life as an image data transfer medium.

"I was a little surprised that in about five years we went from 100% film to nearly zero," Erickson said. "I think it's going to be a lot longer than that for CDs, partly because it's inexpensive to produce CDs and a lot more expensive to produce film copies. I suspect it's going to be at least 10 years before we fully embrace Internet-based transfers."

If it’s round, has a hole in it, and isn’t a bagel or donut in the break room, chances are it’s a CD brought into the practice by a patient. According to Dr. Bradley Erickson from the Mayo Clinic in Rochester, MN, the use of compact discs to transfer diagnostic imaging data has seen a steady increase over the past decade.

Author | Jonathan Batchelor

Articles

CT radiation dose shows wide variance in ED

Unnecessary sequences add to radiation burden

CD data imports show growth, durability